Wet and dry etching methods are widely used to define patterns in semiconductors. Wet etching techniques rely on chemical solutions to carve out features, while dry etching methods utilize the chemical and physical action of ions for material removal. Although wet etching offers the benefits of simplicity and low cost, wet etching methods are inadequate for defining very small features and tend to remove material isotropically, instead of directionally. In contrast, dry etching offers the benefits of anisotropy and tight control over etching rate and feature dimensions. With the increasing complexity and integration of semiconductor electronic and optical devices, dry etching has become a critical process in the dimensional control of vertically etched structures (e.g., mesas).
GaAs and other III-V compound semiconductors are a key component of various photonic and electronic devices, such as lasers, modulators, detectors, amplifiers, passive waveguide devices, heterojunction bipolar transistors (HBTs), and high electron mobility transistors (HEMTs). The fabrication of smooth and vertical mesas in lasers, passive waveguides, and other optical devices based on III-V compound semiconductors is important for reducing scattering and minimizing waveguide propagation losses. In addition, surface roughness can increase non-radiative recombination center levels, which in turn can degrade the internal quantum efficiency of such devices. In electronic devices, surface roughness can introduce additional defect levels into the bandgaps of semiconductors that can diminish electronic performance.
Plasma etching is a widely used dry etching method for GaAs and other III-V compound semiconductors. Among the various plasma etching techniques, reactive ion etching (RIE) and inductively coupled plasma (ICP) are the most common for etching III-V compound semiconductors. ICP provides several advantages over RIE. Because there are two power inputs in the ICP system, the plasma density and the plasma energy may be controlled independently and damage due to ion bombardment can be reduced accordingly. In addition, the chamber pressure in an ICP system is reduced by about an order of magnitude compared to that in an RIE system. ICP etching rates in excess of one micron per minute (1 μm/min) have been achieved for GaAs, but the etched structures often show sidewall damage or off-vertical profiles.